Number portability has not been addressed consistently or completely in VoIP networks. However in the circuit switched networks, various methods have been used. Some of the circuit switched methods are as follows.
In an “all call query” the originating network switch queries a central database (NPDB) for a routing number. This is done for all calls that come into the switch. This routing number is then used to route the call to the destination.
In “onward routing” the call is routed to the destination switch which detects that the dialed number is ported. The destination switch queries a central database (NPDB) to obtain the new routing number and routes the call.
In “query on release” the call is routed with the original dialed digits. The destination network detects that the dialed number is ported and releases the call with a cause code indicating the porting. The originating switch then queries a central database (NPDB) to obtain the new routing number. It uses this number to reroute the call.
In “call drop back”, like the “query on release” case, the call is routed to the destination network. The terminating switch discovers that the dialed number is ported and queries a central database NPDB to retrieve the new routing number. It then releases the call with the routing number in the response. The originating switch uses this routing number to reroute the call.
In all of the these solutions, the logic for querying the database and routing the call is embedded in the switch call processing software. The concept of distributed switching elements is not found in the circuit switched networks.
Thus, there is a need in the art for an improved and more efficient system that has an IMS entity that may support number portability and the routing for E.164 numbers.